I sent you the other pictures of my other glow fish to . It's a 10 gallon tank. I only have the 4. I've changed the water, but I don't know what is wrong with the danao?
In the meantime, do you have any spare filters? or heaters? Or even a quarantine tank? Move her in there if you have a quarantine tank. I you have a spare filter heater and storage box, take half the water from your main tank and put in in there, along with half of it being dechlorinated tap water. Put the filter and heater in and move her in. Put a hiding space in.
If you don't have any thing like that:
You could try an antiseptic medicene, but it might not be worth it to be honest. She looks past saving. Sorry
Again though, what are the water patameters? You can buy test strips.